The genes in the mouse H-2 major histocompatibility complex determine a diversity of functions associated with immune recognition and reaction. Three of these genes, H-2K, H-2D and H-2L encode the major antigens involved in allograft rejection; a feature undoubtedly related to the genetic polymorphism of these H-2 molecules. In addition, these molecules play a role in T-lymphocyte responses to altered cell-surface antigens. These H-2 molecules are integral membrane glycoproteins and are associated on the cell surface with B2-microglobulin. The purpose of this work is to determine the primary structure of these molecules in order that we may better understand their function and mechanism of action. Toward this goal, we are determining the primary structure of each of these molecules from mice of the b and d haplotypes (i.e. H-2Kb, H-2Db, H-2Dd, H-2Ld). The amino acid sequence analysis of H-2Kb is near completion and limited amounts of sequence data are available for the other molecules. In addition, the determination of the primary structure of murine Beta-microglobulin is near completion.